Superabsorbent polymeric materials capable of absorbing large quantities of liquids are known in the art and used in many applications, in particular in sick-care and hygienic products such as wound dressings, diapers, adult incontinence pads, feminine sanitary pads and the like. Prior art methods for producing superabsorbent materials capable of absorbing water are based on the use of highly hydrophilic polymers, such as polyacrylates, polyacrylamides, acrylates and their derivatives, grafted on starch or cellulose. Polymeric molecules are usually crosslinked and form a gel-like three-dimensional network. These methods are described in an article entitled Water-absorbent polymers: a patent survey, published in the Journal of Macromolecular Science, Reviews Macromolecular Chemistry, 1994, C34, 607-662.
The water absorbing capacity (WAC) of water-absorbing polymers can be substantially increased by forming pores (preferably open-cell pores) within the polymer matrix. Prior art methods of making porous polymer matrices are based on foaming the reaction mixture before or during the run of polymerization and/or crosslinking reactions using a blowing agent, such as gases or volatile liquids. A method of making superabsorbent polymer foam having improved absorptive properties is described, for example, in U.S. Pat. Nos. 5,328,935 and 5,338,766 to Vah Phan et at.
Other prior art approaches for forming porous absorbent materials include crosslinking of a multiplicity of precursor particles into an interparticle macroaggregate (U.S. Pat. No. 5,372,766 to Roe), freezing hydrophilic polymers solutions in the form of prenucleated ice sheets with subsequent freeze-drying (PCT publication No. WO 95/05204 to Schonfeldt et al), carrying out polymerization reactions in conditions of a specific type of high internal phase emulsion (U.S. Pat. No. 5,334,621 to Beshouri).
Prior art methods of preparing highly superabsorbent porous materials, also termed herein superabsorbent foams, having high WAC are deficient in some respects. For example, each of the prior art methods can be applied only to polymers of a definite chemical nature. Also, the possibility of fine controlling the parameters of the porous structure are limited, in particular on scaling up these methods for industrial applications.